1. Field of the Invention
The present invention generally relates to an interference measurement method and apparatus for a new carrier type and, more particularly, to an Interference Measurement Resource (IMR) allocation method and apparatus for efficient interference measurement in a downlink in a system supporting a New Carrier Type (NCT).
2. Description of the Related Art
Mobile communication systems have evolved into high-speed, high-quality wireless packet data communication systems to provide data and multimedia services beyond the early voice-oriented services. Recently, various mobile communication standards, such as High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), Long Term Evolution (LTE), and LTE-Advanced (LTE-A) defined in 3rd Generation Partnership Project (3GPP), High Rate Packet Data (HRPD) defined in 3rd Generation Partnership Project-2 (3GPP2), and 802.16 defined in IEEE, have been developed to support the high-speed, high-quality wireless packet data communication services. Particularly, LTE is a communication standard developed to support high speed packet data transmission and to maximize the throughput of the radio communication system with various radio access technologies. LTE-A is the evolved version of LTE to improve the data transmission capability.
Typically, LTE base stations and terminals are based on 3GPP Release 8 or 9 while LTE-A base stations and terminals are based on 3GPP Release 10. The 3GPP standard organization is specifying the next release for more improved performance beyond LTE-A.
The existing 3rd and 4th Generation wireless packet data communication systems (such as HSDPA, HSUPA, HRPD, and LTE/LTE-A) adopt Adaptive Modulation and Coding (AMC) and Channel-Sensitive Scheduling techniques to improve the transmission efficiency. AMC allows the transmitter to adjust the data amount to be transmitted according to the channel conditions. That is, the transmitter is capable of decreasing the data transmission amount for bad channel conditions so as to fix the received signal error probability at a certain level, or increasing the data transmission amount for good channel conditions so as to transmit large amounts of information efficiently while maintaining the received signal error probability at an intended level. Meanwhile, the channel sensitive scheduling technique allows the transmitter to serve the user having a good channel condition selectively among a plurality of users so as to increase the system capacity as compared to allocating a channel fixedly to serve a single user. This increase in system capacity is referred to as multi-user diversity gain.
When using AMC along with a Multiple Input Multiple Output (MIMO) transmission scheme, it may be necessary to take into consideration a number of spatial layers and ranks for transmitting signals. In this case, the transmitter determines the optimal data rate in consideration of the number of layers for use in MIMO transmission.
Recently, research has been conducted to replace Code Division Multiple Access (CDMA) used in the legacy 2nd and 3rd mobile communication systems with Orthogonal Frequency Division Multiple Access (OFDMA) for the next generation mobile communication system. The 3GPP and 3GPP2 are in the middle of the standardization of an OFDMA-based evolved system. OFDMA is expected to provide superior system throughput as compared to CDMA. One of the main factors that allows OFDMA to increase system throughput is frequency domain scheduling capability. As channel sensitive scheduling increases the system capacity using a time-varying channel characteristic, OFDM can be used to obtain more capacity gain using a frequency-varying channel characteristic.
In the OFDMA-based LTE/LTE-A system, control signals such as Physical Downlink Control CHannel (PDCCH), Physical Hybrid Automatic Repeat reQuest Indicator CHannel (PHICH), Physical Control Format Indicator CHannel (PCFICH), and Common Reference Signal occupy a relatively large portion of radio resources. This results in an issue of control signal overhead, power consumption, and resource shortage. The New Carrier Type (NCT) is a technology introduced to minimize the control channel and reference signal overhead and has drawn attention as a promising technology for improving network data throughput and power utilization efficiency in the complex mobile communication environment where macro and small cells coexist.
Typically, a cellular radio mobile communication system is comprised of a plurality of cells distributed within an area. Each cell is centered around a base station responsible for communication with mobile devices or terminals. The base station includes antennas and a signal processing part for providing mobile communication services to the terminals within the cell. Such a system in which the antennas are placed at the center of the cell is referred to as Centralized Antenna System (CAS) and is typical in a normal mobile communication system. In contrast, a system in which the antennas are distributed in the range of the service area of the cell is referred to as Distributed Antenna System (DAS) and is advantageous in providing improved mobile communication service as compared to the CAS.
In an LTE/LTE-A system, Interference Measurement Resource (IMR) is used to improve interference measurement accuracy for DAS as well as CAS. In this way, the LTE/LTE-A system increases the mobile data throughput. Recently, in order to meet the increasing demand for mobile data service, mobile carriers are introducing small cell technology to distribute the data traffic. The introduction of the small cell technology is advantageous to distribute data traffic so as to reduce the load of the network, but also causes problems such as increased control and interference signal overhead.
The LTE-A Release 12 introduces New Carrier Type (NCT) to reduce control channel and common reference signal overhead, thereby improving radio resource utilization efficiency. The NCT is promising for improved radio resource utilization in the network environment where the small and macro cells coexist.